Diodes & transistors worksheet with answers

Free printable Diodes & transistors worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
+−Vs​15 VR = 220 ΩD​I = ?

A 15 V DC source drives current through a 220 Ω resistor in series with a forward-biased silicon diode. Use the constant-drop model with 0.7 V per conducting diode. Find the current I in mA.

Vs = 15 VR = 220 ΩVD = 0.7 V
I = mA
2.Easy
+−5 VR = ?2.1 V25 mA

A yellow LED with a forward voltage of 2.1 V runs from a 5 V supply through a series resistor. Find the resistance R that sets the LED current to 25 mA.

Vs = 5 VVF = 2.1 VI = 25 mA
R = Ω
3.Medium
RC​ = 2.2 kΩβ = 150IC​ = ?RE​ = 680 ΩVCC​ = 15 VR1​ = 47 kΩR2​ = 10 kΩ

An NPN transistor with β = 150 has voltage-divider bias from VCC = 15 V: R₁ = 47 kΩ from VCC to the base and R₂ = 10 kΩ from the base to ground. The collector resistor is RC = 2.2 kΩ and the emitter resistor is RE = 680 Ω. Take VBE = 0.7 V and use the Thévenin equivalent of the divider (do not neglect the base current). Find the collector current IC in mA.

VCC = 15 VR1 = 47 kΩR2 = 10 kΩRC = 2.2 kΩRE = 680 Ωβ = 150
IC = mA
4.Medium
+−12 VR = ?3 × 2.2 V15 mA

3 green LEDs (forward voltage 2.2 V each) are connected in series with a resistor to a 12 V supply. Find the resistance R that sets the current to 15 mA.

Vs = 12 VVF = 2.2 Vn = 3I = 15 mA
R = Ω
5.Hard
V (V)I (mA)0.6555Q = ?

A diode is modelled as 0.65 V in series with 50 Ω (it conducts above 0.65 V). It is in series with a 1000 Ω resistor across a 5 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 5 VR = 1000 ΩV0 = 0.65 Vrd = 50 Ω
ID = mA
6.Hard
V (V)I (mA)0.7533.33Q = ?

A diode is modelled as 0.7 V in series with 25 Ω (it conducts above 0.7 V). It is in series with a 150 Ω resistor across a 5 V supply. Find the operating current ID where the diode line meets the load line.

Vs = 5 VR = 150 ΩV0 = 0.7 Vrd = 25 Ω
ID = mA

Answer key

  1. 1. I = 65 mA
  2. 2. R = 116 Ω
  3. 3. IC = 2.612 mA
  4. 4. R = 360 Ω
  5. 5. ID = 4.143 mA
  6. 6. ID = 24.57 mA

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